Passive dosing dispensers featuring a wide variety of structures and operations are relatively abundant in the prior art. U.S. Pat. No. 4,208,747, which issued to Robert Dirksing on June 24, 1980 (re-examination certificate issued Aug. 16, 1983), discloses a passive dispensing unit for dosing chemical solutions to toilet tank water during a flush cycle, and which utilizes air locks to isolate its chemical solutions from the toilet tank water during quiescent periods. The chemical solutions of the Dirksing reference are dispensed in response to toilet water level changes during a flush cycle.
The prior art also includes dispensing units designed to remove built-up soil deposits in toilets via automatic chemical dispensing devices. U.S. Pat. No. 3,121,236, which issued to F. G. Yadro et al. on Feb. 18, 1964, teaches the metering of chemical compounds into each tankful of water in a flush tank in amounts sufficient to stop further build-up of deposits and to gradually remove pre-existing deposits. The Yadro dispenser comprises an open-ended box having inlet/discharge holes formed in the side walls of the box and containing a block of soluble chemical therewithin. Tank water enters the dispenser as the water level rises at the end of a flush cycle dissolving some of the chemical block to form a solution which is discharged during the next flushing cycle.
Another automatic toilet bowl dispenser is disclosed in U.S. Pat. No. 2,807,807, which issued to R. H. Harper on Oct. 1, 1957. The Harper dispenser includes a flexible bag filled with soluble, solid chemical particles and having a plurality of apertures arranged in a vertically spaced relationship in the bag. The Harper reference alleges that during the first several flush cycles, soluble chemical above the level of the apertures is dissolved to form a relatively concentrated chemical solution with the water in the tank. After the solid particles are dissolved to a level below the apertures, only the top layer of solid particles will be available to form a solution with water entering the bag, thus lowering the amount of solid chemical entering into solution during flush cycles thereafter. The Harper dispenser thereby allegedly provides a high initial concentration of chemicals during the first several flush cycles in the dispenser's operational life, and a lower concentration thereafter. It is believed, however, that the Harper dispenser would actually deliver lower level doses of chemical during the initial flushing cycles, with such levels increasing as more sudden volume could be contained in and dispensed from the flexible bag. The Harper dispenser would thereby fail to provide high initial dosage levels, and lower subsequent dosage levels.
Despite all of the prior work done in this area, as evidenced by the above-cited patents, there remain problems in accurately dispensing high strength doses of chemicals to a toilet bowl during an initial period, and following such initial period dispensing a lesser concentration of chemicals. An economic device was needed to dispense such high strength initial doses of chemical solutions during an initial number of flush cycles, while isolating such chemical solutions from the toilet tank water during quiescent periods between flushes.